Technical noise present in laser systems can limit their ability to perform high fidelity quantum control of atomic qubits. The ultimate fidelity floor for atomic qubits driven with laser radiation is due to spontaneous emission from excited energy levels. The goal is to suppress the technical noise from the laser source to below the spontaneous emission floor such that it is no longer a limiting factor. It has been shown that the spectral structure of control noise can have a large influence on achievable control fidelities, while prior studies of laser noise contributions have been restricted to noise magnitudes. Here, we study the unique spectral structure of laser noise and introduce a metric that determines when a stabilised laser source has been optimised for quantum control of atomic qubits. We find requirements on stabilisation bandwidths that can be orders of magnitude higher than those required to simply narrow the linewidth of a laser. The introduced metric, the χ-separation line, provides a tool for the study and engineering of laser sources for quantum control of atomic qubits below the spontaneous emission floor.

激光系统中存在的技术噪声会限制它们对原子量子位执行高保真量子控制的能力。由激光辐射驱动的原子量子比特的最终保真度是由于激发能级的自发发射。目标是将来自激光源的技术噪声抑制在自发发射底线以下，使其不再是限制因素。已经表明，控制噪声的光谱结构可以对可实现的控制保真度产生很大影响，而先前对激光噪声贡献的研究仅限于噪声幅度。在这里，我们研究了激光噪声的独特光谱结构，并引入了一种度量标准，该度量标准确定稳定的激光源何时针对原子量子位的量子控制进行了优化。我们发现对稳定带宽的要求可能比简单地缩小激光器线宽的要求高几个数量级。引入的度量，χ - 分离线，为激光源的研究和工程提供了一种工具，用于对自发发射层以下的原子量子位进行量子控制。